Add finer grained schema.org type mappings

Inspired by Eoghan Carragáin's patch at
http://vufind.org/jira/secure/attachment/10297/schemaOrg.patch to
provide a mapping for schema.org types, take a similar approach - but
take advantage of RDFa Lite's support for the the typeof property to
contain multiple types, in case we run into a record with both a Book
and MusicRecording, for example.

Signed-off-by: Dan Scott <dan@coffeecode.net>